Bar screen



J. DE KONING Dec. 7, 1965 BAR SCREEN Filed NOV. 21, 1962 United StatesPatent 6 8 Claims. (611.209-314) The present invention relates to ascreen with srceen bars clamped on the side of the feed only. I

Screens of this type are used for screening material containingparticles of widely divergent grain size, such as run-of-mine coal. Theobject is to separate off a considerable portion of the fine materialquickly and in a simple way, so that the classifying screens, handlingthe coarse material, are less heavily loaded.

The known screening devices have the drawback that the slots between thebars frequently get obstructed by particles of about equal size beingpressed into the slots between the bars by the large lumps sliding overthe screen deck. As a result, the capacity of the screening devicedecreases, in consequence of which a large portion of the fine materialis not separated off and the screen has to be frequently stopped forcleaning. It is true that some improvement can be achieved by the use ofshaker screens or vibrating screens. However, this renders the screeningdevice complex and expensive. Furthermore, it has already been suggestedto use bars which are so designed that the slot-width increases in thedirection of flow of the material to be screened. However, owing to thelength of the screen bars, the slots can diverge to a small degree only,so that these screens, too, frequently get obstructed.

This invention has for its primary object the provision of a device forscreening material of widely diverging grain size, which does not getobstructed and can be built as a stationary screen.

This has been achieved in that according to the invention bars of lowand high elasticity are alternately arranged beside each other in such away that the upper surface of the bars having a low elasticity is at ahigher level than that of the bars having a high elasticity.

The size to which the cut is made is substantially determined by thedistance between the elastic and the more rigid bars. When a particlegets jammed between these bars, the material sliding over the surface ofthe screen will exert such a force on this particle that the elastic baris bent or deflected sideways. As a result, the slot between the barswill widen and diverge towards the discharge end. The particle jammedbetween the bars will now fall through the screen or be pushed forwardsby the material sliding over the screen and fall through the screen at apoint where the slot is sufficiently wide. In this way, the screen keepsitself clean, so that it can no longer be obstructed. As the uppersurface of the elastic bars is at a lower lever than that of the morerigid bars, the big heavy lumps are carried by the latter, so that theelastic bars, which are of course weaker, are not loaded by them.

By preference, the elastic bars are circular in section so as to enablethem to deflect to the same extent in all directions. The other bars arestrengthened vertically, so that their stiffness in this directionsuflices for carrying the weight of the big lumps present in thematerial to be screened. These bars preferably consist of a bar ofcircular section and a bar of rectangular section having its shorterside welded onto the undersurface of the firstmentioned bar, thehorizontal centerlines of the circular section part and of the elasticbars being at the same level. In this way, it is achieved that bendingof an elastic bar is always attented with an increase of the slot width"ice between the bars. If desired, the rigid bars may be clamped orsupported on both ends, while they may furthermore be designed so as tobe capable of deflecting sideways if necessary.

The invention is further explained with reference to the embodimentshown in the drawing, in which:

FIG. 1 is a perspective view of a screen according to the invention;

FIG. 2 is a perspective view of -a screen section drawn to a largerscale; and

FIG. 3 shows a cross-sectional view of the screen bar attachment.

The material to be screened, for instance run-of-mine coal, is suppliedto a pre-grading screen 2 by a belt conveyor 1. The pre-grading screenis provided with a number of Stepped screen sections 3 mounted betweentwo side walls 4, only one of which is shown in the drawing to allow abetter view of the construction.

Each of the screen sections comprises a bridge 5 with downwardly flangededges 6 in which holes 7 are drilled for fastening the bridges to theside walls 4. The ends of screen bars 8 are welded to the undersurfaceof the bridges at regular intervals. Each of the screen bars consists ofa round bar 9 and a fiat bar 10. Each flat bar 10 is rectangular incross section and right triangular in longitudinal section with itsshorter side being welded onto the undersurface of the associated roundbar 9, so that the screen bar is stiffened vertically. Near the bridgethe height of the bar 10 is greater than near the free end. Between thebars 8 thin bars 11 of circular cross-section are provided. One of theends of these bars is fastened to the unde'rsurface of the bridge bymeans of a clamping plate 12 and bolts 13, so that the bars can bequickly replaced when worn. Welded against the undersurface of thebridge at the points where the thin bars 11 are to be mounted arefilling plates 14 so that, after the bars have been clamped intoposition, the upper surface of these bars is at a lower lever than thatof the bars 8. The thickness of the filling plate is such that thehorizontal centerlines of the bars 9 and 11 are at the same level. Ifthe bar 11 bends, the slot between the two bars widens, so that aparticle which has got jammed between the bars cannot remain there, butfalls through the screen.

Via a feed plate 15 the material supplied slides onto the bridge 5 ofthe first screen section. The bars attached to this bridge are set atsuch an angle that the material will slide along the screen deck by itsown weight. A suitable angle of slope for dry-screening is 20 to 25. Thedistance between the bars 8 and 11 in the embodiment is 60 mm., theelastic bars 11 having a diameter of 16 mm. and a length of 600 mm.-Owing to the elasticity of the bars 11 the effective size to which thecut is made exceeds the actual slot width. When four screen sectionswith a width of l m. were arranged in series and operated under a loadof 2000 t./h., the undersize delivered into chute 16 Was found tocontain of the particles with a size smaller than 90 mm. Via a chute 17the oversize is fed from the screening device to a moving screen whichhas to perform a high precision separation at 90 mm. The load of thisscreen is considerably reduced by the application of the pre-gradingscreen according to the invention, so that a small and, consequently,cheap screen will suffice. The load of the screen described in theexample was found to be only 20% of the weight of the material suppliedto device 2.

As the length of the bars is limited, and the amount of materialsupplied is rather large, only part of the fine material will have beenseparated off after the material has passed the first section.Consequently, a number of sections are arranged in series, in such a Waythat material flowing over the lower end of a preceding section fallsonto the bridge of a following section, for example the bars endsclamped to this bridge underlie the free ends of the bars of thepreceding screen section. This bridge not only partly underlies theupstream bar free ends, but also partly overlaps the downstream bars,i.e., the bridge projects or extends somewhat forwardly of the pointwhere the bars are clamped on the underside of the bridge, as theelasticity of the bars at a short distance from the clamped ends isstill too low to produce the desired effect. Furthermore, the height ofthe free ends of the bars over the following bridge is such thatparticles hanging between the bars at this point cannot be arrested bythe bridge and get stuck there.

What is claimed is:

1. A device for screening and sizing material comprising a stationaryscreen having a plurality of screening bars secured only at theirmaterial feed end and extending beside each other in the material feeddirection, said bars being alternately of high and low elasticity, andmeans for securing said bars at their material feed ends and for causingthe upper surface of the bars of low elasticity to be at a higher levelthan the upper surface of the bars of high elasticity throughout thelengths of the respective bars.

2. A device as in claim 1 wherein said bars of high elasticity arecircular in section.

3. A device as in claim 1 wherein each of the bars of low elasticityinclude a respective circular section and secured to the undersurfacethereof a rigidizing rectangular section.

4. A device as in claim 3 wherein the aXes of the high elasticity barsand of the low elasticity circular sections are at the same level.

5. A device as in claim 3 wherein said bars of high elasticity arecircular in section.

6. A device as in claim 1 wherein said securing means includes a bridgeto the underside of which all of said bars are clamped at their saidmaterial feed ends, said bridge extending in the material feed directionbeyond the point where the bars are clamped a predetermined distancesufiicient for desired screening.

7. A device as in claim 6 including a plurality of screens each asrecited therein disposed in series with the clamped ends of the bars ofeach screen being under the free ends of the bars of the precedingscreen.

8. A device as in claim 7 wherein each of the said bars of highelasticity are circular in section, each of the bars of low elasticityhaving a first portion of circu lar cross section and a second portionof rectangular cross section and a generally triangular longitudinalcross section with its shorter side being welded onto the undersurfaceof the respective first portion so that the longer end of the secondportion is adjacent the bridge to which the bar is clamped, thehorizontal centerlines of the circular section of the low elasticitybars being at the same level.

References Cited by the Examiner UNITED STATES PATENTS 760,590 5/ 1904Vodra 209-393 850,447 4/ 1907 Shumaker 209-314 910,904 1/ 1909 Chipera209-405 2,443,176 6/ 1948 Banning 209-393 FOREIGN PATENTS 1,263,8735/1961 France. 1,017,840 10/ 1957 Germany.

122,098 12/ 1957 Russia.

HARRY B. THORNTON, Primary Examiner.

HERBERT L. MARTIN, Examiner.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No 3 221,877 December 7 1965 Jacob de Koning It is certified that error appearsin the above identified patent and that said Letters Patent are herebycorrected as shown below:

In the heading to the printed specification, lines 3 and 4 "75 FransErenslands, Geleen, Netherlands" should read Gelee Netherlands, assignorto Stamicarbon N.V., Heerlen, Netherlands Signed and sealed this 3rd dayof March 1970 (SEAL) Attest:

Edward M. Fletcher, Jr. WILLIAM E. SCHUYLER, JR

Attesting Officer Commissioner of Patents

1. A DEVICE FOR SCREENING AND SIZING MATERIAL COMPRISING A STATIONARYSCREEN HAVING A PLURALITY OF SCREENING BARS SECURED ONLY AT THEIRMATERIAL FEED END AND EXTENDING BESIDE EACH OTHER IN THE MATERIAL FEEDDIRECTION, SAID BARS BEING ALTERNATELY OF HIGH AND LOW ELASTICITY, ANDMEANS FOR SECURING SAID BARS AT THEIR MATERAL FEED ENDS AND FOR CAUSINGTHE UPPER SURFACE OF THE BARS OF LOW ELASTICITY TO BE AT A HIGHER LEVELTHAN THE UPPER SURFACE OF THE BARS OF HIGH ELASTICITY THROUGHOUT THELENGTHS OF THE RESPECTIVE BARS.